Piano action

ABSTRACT

A key extension member pivoted about a fulcrum on a base has a first end portion connected to the key and a second end portion carrying a pin for pivotally mounting a hammer which has a striking portion for striking a sensor element, and a free end portion. The free end is retained by a jack mounted on the base, causing the hammer to rotate and strike the sensor when the pin moves up during depression of the key. A jack operating plate forming an integral part of the key extension member causes the jack to release the free end of the hammer after the sensor has been struck. In one embodiment of an electronic piano, the hammer causes the selector arm of a selector switch to move from a first to a second position. During the time required for this movement a previously charged capacitor discharges and the voltage remaining on the capacitor is applied to circuitry which varies the volume of the output tone accordingly. Mechanical and/or electrical dampers are operated by the jack or the key extension member in synchronism with the movement of the key.

United States Patent [1 1 Morita PIANO ACTION [75] Inventor: Masanori Morita, Osaka, Japan [73] Assignee: Roland Corporation, Osaka, Japan [22] Filed: Oct. 21, 1974 [21] Appl. No.: 516,218

[30] Foreign Application Priority Oct. 26, I973 48-12112? Aug. 5, 1974 Japan 49-90118 [52] 11.8. CL 84/237; 8411.01; 8411.26 [51] Int. Cl. G10C 3/18 [58] field oISearch 8411.01, 1.04, 1.06, 1.13, 84/ 1.26, D16. 6, 423, 426, 427, 433, 171, 216, 217, 218, 236, 243, 404, 242, 241, 249, 237, 240

[ References and UNITEDSTATES PATENTS 591,887 10/1897 84/237 2,974,555 3/1961 84/216 X 3,208,326 9/1965 84/236 X 3,248,470 4/1966 84/ 1.26 X 3,514,522 5/1970 8411.26 X 3,516,321 6/1970 84/].26 X

[ 51 Dec. 23, 1975 Primary Examiner-L. T. Hix Assn-tam Examiner-U. Weldon Attorney, Agent, or Firm-Kurt Kelman [57] ABSTRACT A key extension member pivoted about a fulcrum on a base has a first end portion connected to the key and a second end portion carrying a pin for pivotally mounting a hammer which has a striking portion for striking a sensor element, and a free end portion. The free end is retained by a jack mounted on the base, causing the hammer to rotate and strike the sensor when the pin moves up during depression of the key.

A jack operating plate forming an integral part of the 9 Clairm, 14 Drawing Figures US. Patent Dec. 23, 1975 Sheet 1 of 5 3,927,594

US. Patent Dec. 23, 1975 Sheet 2 of5 3,927,594

US. Patent Dec. 23, 1975 Sheet 3 of5 3,927,594

mechanical elect rfcal Fig. 7 I

transducer cum/1t te circuit P0W6r 0. .Sd m er edal switch source a P (-asv) US. Patent Dec. 23, 1975 Sheet4of5 3,927,594

9 QPQ Q muk b 3mm; E GaE US. Patent D626. 23, 1975 Sheet 5 ms 3,927,594

Fig. 73

PRIOR AR T S a 3a a 21? 2 {1 V musi al signal source G gdtc circuit 20' 0.1 .6. dzlmper peda l (Sh/Itch PIANO ACTION This invention relates to a keyboard device for keyed instruments as, for example, electronic pianos, and particularly to such a device having a lesser number of elements for performing the necessary functions of such an instrument as compared to those of the prior art.

Characteristics generally demanded in a keyed instrument are the following:

I. A sufficiently short response time to allow a quick repetition of a given note or tone,

2. Hammer rebound should not occur;

3. The force with which the string is struck should be proportional to the force with which the key is struck,

4. The touch of the key or the sensibility of the finger tip should be delicately related to the characteristics of the instrument.

The device according to this invention successfully satisfies the above requirements.

The keyboard device according to this invention will now be described in detail, and with reference to the accompanying drawing, in which FIG. 1 is a general sectional view of a first embodiment of the key mechanism or action according to this invention;

FIG. 2 is a plan view of the mechanism shown in FIG.

FIG. 3 is a perspective view of the key extension member shown view in FIG. 1

FIGS. 4, 5 and 6 are illustrations of the sequence of operation of the device shown in FIG. 1,

FIG. 7 is a circuit diagram showing a preferred embodiment of the electronic circuitry interacting with the key mechanism according to this invention;

FIG. 8 are wave form diagrams for the circuit of FIG.

FIG. 9 is a general sectional view of a second preferred embodiment of this invention;

FIG. I is perspective view illustrating the operation of the device of FIG. 9;

FIG. 11 shows a conventional electronic circuit including a switch coupled to the key mechanism;

FIG. 12 is a diagram for illustrating the principle of operation of the device in FIG. 11;

FIG. 13 shows the construction of the well known key operated switch; and

FIG. 14 is a diagram of the electric circuit for the embodiment shown in FIG. 9.

A preferred embodiment of the present invention will now be described with reference to the drawing.

As may be seen in FIGS. 1 through 3, a key extension member I with flat sides disposed vertically is connected to a key 2 at its front (first end portion), said member 1 having a notch 3 at the middle bottom portion thereof. The entirety of the member 1 is supported on a fulcrum 6, with the notch 3 fitted on said fulcrum 6 at the front side of the vertical portion of an L-guide disposed on a base plate 4, the member 1 being kept in a state wherein it is pushed to the fulcrum 6 by means of a spring 7. A lateral shift of the member I as would be produced when a finger strikes the key 2 is prevented by a guide 8 provided on the base plate 4. A receiver block 9 for the key 2 is also disposed on said base plate 4. 0n the upper rear end of the member 1 is provided a hammer pin 10, on which a hammer I1 is rotatably pivoted. An inverted T-jack 12 (one embodiment of restraining means) having a hook 13 at the upper end thereof is rotatably pivoted on a pin 14 positioned in a rear portion of the base plate 4, and a spring 15 is provided to give a clock-wise torque to said jack around the pin 14, whereby the tip 16 of the hammer 11 receives a soft clockwise thrust. A jack operating plate 17 consisting of a horizontally bent lug in the rear portion of the member 1 is disposed against a downward protrusion 19 at the right end of the horizontal base 18 of jack 12. A back check pin 20 is provided on the bottom of the member 1 at the rear side of notch 3. A back check 21 is pivotally supported at the bottom on said back check pin 20. The back check 21 has a C shaped portion 23 at the rear side of the pin 20, and the tip of the back check driving plate 24 is made to enter into the cut-out 22 of the C-portion, said driving plate 24 being a portion of the base plate 4 bent to form a horizontal ledge thereof. A damper switch 25 is provided at the rear of base plate 4. Damper switch 25 is adapted to be operated by the left end portion 26 of horizontal base 18 of T-jack 12 as the jack swings around pin 14. Damper switch 25 is interconnected with the electronic circuitry of the piano.

The damper switch 25 may also be disposed so as to be driven by an upper supporter bar 30. A mechanicalelectrical transducer includes a sensor element 27 which is, for example, a piezo-electric element. The mechanical-electric transducer is adapted to generate an output voltage corresponding to the intensity of the force with which the sensor element is struck. The sensor of course is struck by hammer 11 when the corresponding key is depressed. A damper cushion 28 secured to a supporter bar 30 is normally in contact with sensor element 27 for gently damping its vibration. When the keyboard is struck, damper cushion 28 is removed from contact with sensor 27, allowing the latter to vibrate freely. (as shown in dashed lines in FIG. I and FIG. 5). Thus the damper cushion 28 is adapted to prevent or to release the vibration of the sensor 27 in accordance with the up and down motion of the key 2 when the same is struck.

Now the operation of the device according to this invention constituted as described in the above will be illustrated with reference to further drawings, in which FIGS. 4, 5 and 6 show aspects of key operation, FIG. 4 showing the mutual relation of parts before the key is struck.

I. If the key 2 be struck from above along the arrow 0 (FIG. 4), the member I will make a clockwise swing around the fulcrum 6, and the hammer ll pivoted at the hammer pin 10 is caused to move upwards. Since, at that instant, the rear end 16 of the hammer 11 is engaged with the upper end hook 13 of the jack 12, the hammer I I will make a counter clockwise swing (along the arrow b) around the hammer pin 10 to strike the sensor element 27 with the protrusion 31 at the front end thereof. At this moment the damper cushion 28 no longer touches sensor element 27 (refer to FIG. 5).

2. A moment before the key 2 has been lowered entirely, the jack operating plate 17 formed on the member I lifts the jack l2 upwards in opposition to the elastic force of the spring 15 thereby causing it to retate counter-clockwise around the pin 14 (along the arrow 0, FIG. 5). End 16 of the hammer 11 will therefor be released from hook 13. Now the hammer 11, after striking the sensor 27, will rotate clockwise around the hammer pin it) causing its right end to move downwards. However, the pin 20 provided on the member 1 will, due to the striking of the key, move upward, as will the back check 21 pivoted on said pin 20. The back check 21 will perform a counter clockwise rotation (along the arrow d, FIG. 5) up to a vertical position, thereby causing the upper edge of the cut-out 22 of the back check to abut on the back check driving plate 24. The upper end of the back check 21 will thus prevent the hammer II from going downwards, thereby keeping said hammer II from striking twice. Further, due to the counter-clockwise rotational displacement of the jack 12, the bottom rear end 26 of the jack 12 will cause the damper switch 25 to be opened. Thus, there is provided an intercoupled mechanism between the damper switch 25 and the damper cushion 28.

3. When the finger tip has left the key, the key will start a restoring motion along the arrow a in FIG. 6 due to the elastic force of the spring. One end of hammer 11 is still held by back check 21. Pin travels downward. When it reaches a sufficiently low position, jack 12 will pivot under the elastic force of spring 15 and end hook 13 will engage the tip end 16 of hammer 11 (FIG. 6). Accordingly, the sensor 27 may be struck against by the hammer just as stated in the above item (I), even if the key is struck again when it has risen to an intermediate position only. And as the back check 21 is pivotally supported at the bottom portion thereof on the pin 20, but the tip of back check driving plate 24 enters the cut-out 22 of the back check, the back check 21 will, swing clockwise (along arrow e in FIG. 6) when the key 2 moves up (along arrow d in FIG. 6). Accordingly, hammer 11 will be released and restored to the position shown in FIG. 4. The damper switch 25 will also be restored to the closed state, and the damper cushion 28 will give a soft thrust onto the sensor 27. Further, the damper switch 25 will be opened while key 2 is pushed down after having been struck, but it will be closed when the finger tip has left the keyboard, whereby a damper effect will be obtained by means of an electronic circuit incorporated into the electronic keyboard instrument. An example of such an electronic circuit is illustrated in FIG. 7, wherein reference numbets 1, 2, 6, 10, ll, 25, 27, and 31 indicate the same members as shown in FIG. 1. Reference number 32 refers to a mechanical electrical transducer circuit, 33 a gate circuit, 34 a musical scale signal oscillator, 35 an amplifier, and 36 a speaker. Now, if the key 2 be struck (along the arrow 0), the hammer 11 will swing around the pivot pin 10 to make a quick upward shift along the arrow b, damper switch 25, coupled to the hammer 11, being opened accordingly. The front end protrusion 31 of the hammer 11 will then strike sensor 27. In the embodiment illustrated in FIG. 7, a capacitive type pick up is shown; that is, mechanical displacement of sensor 27 causes a corresponding variation in its capacity. This variation in capacity is applied to the mechanical electrical transducer circuit 32, causing a voltage proportional to the variation of capacity to be applied to the gate circuit 33. On the other hand, a musical scale signal as shown in FIG. 8a which is furnished by the musical scale signal generating circuit 34 to the gate circuit 33 will be controlled by this voltage which corresponds to the force with which the key was struck and, after amplification in amplifier 35, will cause a musical sound having an amplitude and attenuation characteristic corresponding to the keyboard beating (as shown in FIG. 8b) to be furnished by speaker 36, following amplification in amplifier 35. If the finger tip is removed from the keyboard at time I in FIG. 8b, the hammer 11 will immediately close the damper switch 25 thereby creating the musical sound shown in FIG. 80. This constitutes an adequate damping effect. In FIG. 7 may further be found resistors RI-RS, transistors Trl, Tr2 and Tr3, condenser Co, diode D, power source E, E, Collector voltage Co of Transistor Tr3 and a damper pedal switch D.P.S.

In the above examples a piezoelectric element or a capacitive pick-up is utilized as the sensor 27, but it may be replaced by a mechanical vibrator like a sensor string or a reed, which may readily be utilized as an action member for a general keyboard instrument other than an electronic instrument.

FIG. 9 shows the constitution of the second embodiment of this invention in a sectional view, wherein, instead of a piezo-electric element 27 or other mechanical vibrator (string, reed or the like), is provided a lever switch S in a space above the member 1 in the vicinity of the hammer pin 10. At the time a key is struck, hammer 11 will make an upward swing around the pin 10, and a striking portion 37 provided on the hammer 11 in the neighborhood of the pivot pin 10 will strike the movable lever 38 of said lever switch S, whereby the lever switch will be changed over from the contact A to the contact B, which state may be seen in FIG. 10. As movement of the key extension member 1 due to the striking of the key is added to the swinging motion of the hammer 1 around the pin 10, the effect upon the lever switch S will correspond to a displacement of the key added to an acceleration thereof. The variation of motion as stated above is analogous to the variation of the force on a string being struck by a key of a piano. Further, since the striking portion 37 is positioned in the vicinity of the hammer pin 10, the stroke thereof is short, so that the lever switch S would not be subject to any substantial shock. Accordingly there is no danger to damage of the switch and the shock to a finger striking a key will also be slight. Therefore, it may be seen that the variation of speed of transference from contact A to contact B of the lever switch S, or the variation of the striking strength force would sufficiently represent the operating action of the key of a piano. And, by combining the above stated lever switch with an electric circuit, well known in itself, as that seen in FIG. 11, a unique accent due to the acceleration-of the hammer of the piano keyboard, that has never before been depictable, may be realized. In FIG. 11 is shown an electric circuit for making a touch sense by detecting a charged potential of a time constant circuit consisting of a condenser C and a resistor R9, wherein an output signal from a musical signal source V is controlled by a gate circuit G, the output voltage of a transistor 0 being utilized as the controlling signal. The lever switch S is coupled with the key, whereby it will be switched over from contact A to contact B by the striking of a key. The time necessary for above switch-over substantially corresponds to the force with which the key was struck. In other words, when the key is struck with great force, the switch lever will be transferred from contact A to contact B in a short time and before the potential across the condenser C, which is discharging, has been lowered substantially so that contact B will be supplied with a relatively high potential. But when the key is struck with a soft touch, said transference of the switch will take considerably longer, thereby lowering the potential across the condenser C, so that contact 8 will be supplied with a relatively low potential. FIG. I2 is a graph showing the relation between condenser potential and discharge time. As the time TI is short when the key is struck with great force, the relatively high potential Vx at, point X will be delivered to the contact B, but, as the time T2 is long when the key is struck with a soft touch, the potential Vy at point Y will be delivered to the contact B. Now considering the action operating of a piano keyboard, the hammer would be accelerated in accordance with the force with which the key is struck, so that the force striking the string would also be acceleratingly increased. With the constitution of the key switch of prior art as shown in FIG. 13, the speed of the transference of the switch would merely be proportioned to the speed of keyboard striking, and no accent due to the accerelation of the hammer of and piano keyboard is, therefore, represented. The purpose of this invention is to provide a keyboard switch for an electronic piano, that may be made at low cost, and that will operate reliably with an excellent touch sense.

Now again with reference to FIG. 9, the operation of the electric circuit of FIG. 14 will be explained, when utilizing the key arrangement shown in FIG. 9. In the circuit shown in FIG. 14, the emitter electrode of a transistor Q as shown in FIG. 11 is connected through the resistor R and a diode D1 to one terminal of the damper switch 25, the other terminal of which is connected through the damper pedal switch D.P.S. to ground potential. Transistor Q is switched to the conductive state charging condenser C, when lever 38 makes contact with contact B. The switching of lever 38 from contact A to contact B takes place when striking of the key causes hammer 11 to pivot, thereby causing projection 37 to strike lever 38. The striking of the key also causes jack 12 to pivot, opening damper switch 25. The potential across condenser C when transistor 0 becomes conductive varies, as described above, with the time required for lever 38 to travel from contact A to contact B. The corresponding voltage at the emitter of transistor 0, i.e. the voltage controlling gate circuit G, is substantially the same as that across condenser C while transistor 0 is conductive and switch 25 is open. When the finger tip leaves the key, damper switch 25 closes. The remaining charge on the condenser C] will be discharged within a short interval through the resistor R10, diode D1, damper switch 25, and damper pedal switch D.P.S., whereby a damping effect will be produced. The key frame I is further provided with a jump preventer 39 which will effectively prevent any jump of the hammer 11, as would be produced when it makes an upward swing.

In conclusion the advantages of this invention, of which two embodiments are illustrated above, are noted as follows:

I. The keyboard device, wherein the hammer pin 10 is integrally pivoted on the key extension member 1 and the back check 21 of the hammer is pivoted swingably thereon 1, may be simply manufactured by punching out a single metallic plate and by press-forming as shown in FIG. 3 to successfully perform any necessary function of a keyboard instrument as stated above, so that it may be utilized for a wide field of keyboard instruments including the electronic piano.

2. In the first embodiment of this invention as shown in FIG. I, the vibration of the sensor 27 due to the action of key member I is mechanically damped by means of the damper cushion 28, and is also electrically 6 damped through the damper switch 25, so that a perfect damping effect is attained.

3. In the second embodiment of this invention as shown in FIG. 9, the sensor 27 of the first embodiment (FIG. I) is replaced by the lever switch S provided in the vicinity of the pivotal pin 10 of the hammer 11, whereby the force of the hammer striking the lever switch consists of the motion of the key due to keyboard striking added to an acceleration due to the swinging motion of the hammer around the pin 10, so that there may be obtained any loud or soft tones corresponding to to the variation of tone strength resulting from the striking of the key in a conventional piano. Further, the shock transmitted to the switch by the hammer is very small, so that there is no danger of damage of the switch, and the finger feels but a very slight shock when striking a key.

What I claim is:

1. In a musical instrument having at least one key adapted to move from a first to a second position upon external activation and further having sensor means for creating a sound when struck, a key action comprising, in combination, a base; a key extension member pivotally supported on said base and having a first end portion connected to said key whereby said key extension member moves in correspondence to the movement of said key, a projecting portion, and a second end portion; striking means pivotally mounted on said second end portion and having a free end portion adari ed to receive a restraining force and a striking portion adapted to rotate from a rest position to a striking position striking said sensor means upon movement of said second end portion of said key extension member while said free end portion is acted upon by said restraining force; and restraining means mounted on said base and having a restraining portion for applying said restraining forces to said free end portion of said striking means while said key moves from said first to said second position, and an activating portion adapted to cooperate with said projecting portion of said key extension member to disengage said restraining portion of said restraining means from said free end portion of said striking means after striking of said sensor means, whereby said striking means rotates back toward said rest position following the striking of said sensor means.

2. A musical instrument as set forth in claim 1, wherein said second end portion of said key extension member includes a pin; and wherein said striking means is rotatably mounted on said pin.

3. A musical instrument as set forth in claim 2, wherein said restraining means comprise an inverted T-jack having an upper end portion for receiving said free end portion of said striking means and applying said restraining forces thereto, and having a horizontal base having a first horizontal end portion positioned relative to said projecting portion of said key extension member in such a manner that said projecting portion exerts a force on said first horizontal end portion following the striking of said sensor means by said striking means, said inverted T-jack further having a second horizontal end portion, said restraining means further comprising means for pivotally mounting said inverted T-jack on said base in such a manner that application of said force to said first horizontal end portion causes said inverted T-jack to rotate from an original position wherein said restraining force is applied to said striking means to a release position wherein said upper end portion is disengaged from said free end portion of said striking means, and spring means connected between said base and said inverted T-jack for returning said inverted T-jack to said original position following disengagement of said horizontal portion of said key extension member from said first horizontal end portion of said horizontal base of said inverted T-jack.

4. A musical instrument as set forth in claim 1, further comprising back check means mechanically connected to said base and said key extension member for restraining said striking means in an intermediate position between said rest and striking position while said key is in said second position, thereby preventing a rebound of said striking means, and for releasing said striking means to return to said rest position during movement of said key from said second to said first position.

5. A musical instrument as set forth in claim 4, wherein said back check means comprise a back check pin forming an integral part of said key extension member, a back check plate forming part of said base, and a back check pivotally mounted on said pin and having a C shaped portion for receiving at least a part of said back check plate, said back check being mounted relative to said striking means in such a manner that said back check pivots from a first position disengaged from said striking means to a second position preventing the movement of said striking means while said key moves from said first to said second position.

6. A musical instrument as set forth in claim 1, wherein said sensor means include a sensor element adapted to be struck by said striking means; further comprising damping means for damping the movement of said sensor element when in contact therewith, and means for mechanically coupling said damping means to said key extension element in such a manner that said damping means is in contact with said sensor element only when said key is in said first position.

7. A musical instrument as set forth in claim 6, wherein said sensor element is a capacitive pick-up having a capacitance varying as a function of force applied thereto; and wherein said sensor means further comprise first circuit means connected to said capacitive pick-up for furnishing an output voltage having an amplitude varying as a function of said capacitance tone signal furnishing means for furnishing a tone signal having a predetermined frequency, and gate circuit means having a signal input connected to said tone signal furnishing means, a gating input connected to said first circuit means and an output, for furnishing a gated tone signal at said output, said gated tone signal having a frequency corresponding to said predetermined frequency and an amplitude corresponding to said amplitude of said output voltage, and electroacoustic transducer means connected to said output of said gate circuit means for furnishing an audible tone corresponding to said gated tone signal.

8. A musical instrument as set forth in claim 3, wherein said sensor means comprises a sensor element adapted to be struck by said striking means and furnishing an output signal corresponding to the magnitude of the force applied thereto, and transducer means connected to said sensor means for converting said output signal into a corresponding audible tone; further comprising a damper switch electrically connected to said transducer means and mounted on said base in operative proximity to said second horizontal end portion of said horizontal base of said inverted T-jack in such a manner that said second horizontal end portion operates said damper switch to a state preventing production of said audible tone when said restraining means is in said original position and operates said damper switch to a state permitting said furnishing of said audible tone when said restraining means moves from said original to said release position.

9. A musical instrument as set forth in claim 1, wherein said striking means comprise a hammer adapted to pivot about said pin and having a striking portion positioned in close proximity to said pin; and wherein said sensor means comprise a selector switch having a selector arm moving from a first to a second position under action of said striking means, and transducer means connected to said selector switch for furnishing an audible tone having an amplitude varying as a function of the time required for said selector arm to move from said first to said second position. 

1. In a musical instrument having at least one key adapted to move from a first to a second position upon external activation and further having sensor means for creating a sound when struck, a key action comprising, in combination, a base; a key extension member pivotally supported on said base and having a first end portion connected to said key whereby said key extension member moves in correspondence to the movement of said key, a projecting portion, and a second end portion; striking means pivotally mounted on said second end portion and having a free end portion adapted to receive a restraining force and a striking portion adapted to rotate from a rest position to a striking position striking said sensor means upon movement of said second end portion of said key extension member while said free end portion is acted upon by said restraining force; and restraining means mounted on said base and having a restraining portion for applying said restraining forces to said free end portion of said striking means while said key moves from said first to said second position, and an activating portion adapted to cooperate with said projecting portion of said key extension member to disengage said restraining portion of said restraining means from said free end portion of said striking means after striking of said sensor means, whereby said striking means rotates back toward said rest position following the striking of said sensor means.
 2. A musical instrument as set forth in claim 1, wherein said second end portion of said key extension member includes a pin; and wherein said striking means is rotatably mounted on said pin.
 3. A musical instrument as set forth in claim 2, wherein said restraining means comprise an inverted T-jack having an upper end portion for receiving said free end portion of said striking means and applying said restraining forces thereto, and having a horizontal base having a first horizontal end portion positioned relative to said projecting portion of said key extension member in such a manner that said projecting portion exerts a force on said first horizontal end portion following the striking of said sensor means by said striking means, said inverted T-jack further having a second horizontal end portion, said restraining means further comprising means for pivotally mounting said inverted T-jack on said base in such a manner that application of said force to said first horizontal end portion causes said inverted T-jack to rotate from an original position wherein said restraining force is applied to said striking means to a release position wherein said upper end portion is disengaged from said free end portion of said striking means, and spring means connected between said base and said inverted T-jack for returning said inverted T-jack to said original position following disengagement of said horizontal portion of said key extension member from said first horizontal end portion of said horizontal base of said inverted T-jack.
 4. A musical instrument as set forth in claim 1, further comprising back check means mechanically connected to said base and said key extension member for restraining said striking means in an intermediate position between said rest and striking position while said key is in said second position, thereby preventing a rebound of said striking means, and for releasing said striking means to return to said rest position during movement of said key from said second to said first position.
 5. A musical instrument as set forth in claim 4, wherein said back check means comprise a back check pin fOrming an integral part of said key extension member, a back check plate forming part of said base, and a back check pivotally mounted on said pin and having a C shaped portion for receiving at least a part of said back check plate, said back check being mounted relative to said striking means in such a manner that said back check pivots from a first position disengaged from said striking means to a second position preventing the movement of said striking means while said key moves from said first to said second position.
 6. A musical instrument as set forth in claim 1, wherein said sensor means include a sensor element adapted to be struck by said striking means; further comprising damping means for damping the movement of said sensor element when in contact therewith, and means for mechanically coupling said damping means to said key extension element in such a manner that said damping means is in contact with said sensor element only when said key is in said first position.
 7. A musical instrument as set forth in claim 6, wherein said sensor element is a capacitive pick-up having a capacitance varying as a function of force applied thereto; and wherein said sensor means further comprise first circuit means connected to said capacitive pick-up for furnishing an output voltage having an amplitude varying as a function of said capacitance tone signal furnishing means for furnishing a tone signal having a predetermined frequency, and gate circuit means having a signal input connected to said tone signal furnishing means, a gating input connected to said first circuit means and an output, for furnishing a gated tone signal at said output, said gated tone signal having a frequency corresponding to said predetermined frequency and an amplitude corresponding to said amplitude of said output voltage, and electro-acoustic transducer means connected to said output of said gate circuit means for furnishing an audible tone corresponding to said gated tone signal.
 8. A musical instrument as set forth in claim 3, wherein said sensor means comprises a sensor element adapted to be struck by said striking means and furnishing an output signal corresponding to the magnitude of the force applied thereto, and transducer means connected to said sensor means for converting said output signal into a corresponding audible tone; further comprising a damper switch electrically connected to said transducer means and mounted on said base in operative proximity to said second horizontal end portion of said horizontal base of said inverted T-jack in such a manner that said second horizontal end portion operates said damper switch to a state preventing production of said audible tone when said restraining means is in said original position and operates said damper switch to a state permitting said furnishing of said audible tone when said restraining means moves from said original to said release position.
 9. A musical instrument as set forth in claim 1, wherein said striking means comprise a hammer adapted to pivot about said pin and having a striking portion positioned in close proximity to said pin; and wherein said sensor means comprise a selector switch having a selector arm moving from a first to a second position under action of said striking means, and transducer means connected to said selector switch for furnishing an audible tone having an amplitude varying as a function of the time required for said selector arm to move from said first to said second position. 